FILE - In this May 20, 2013 file photo, Buffalo Bills new defensive coordinator Mike Pettine looks on during an optional NFL football workout in Orchard Park, N.Y. When it comes to putting together his defense, Pettine's intention is to keep opponents guessing. (AP Photo/David Duprey, File)

FILE - In this May 20, 2013 file photo, Buffalo Bills new defensive coordinator Mike Pettine looks on during an optional NFL football workout in Orchard Park, N.Y. When it comes to putting together his defense, Pettine's intention is to keep opponents guessing. (AP Photo/David Duprey, File)

If that leads to some confusion among the Bills in identifying what position they're playing, Pettine's fine with that, too.

"'I don't know,'" he said, smiling, "is a good answer."

Pettine was referring to comments made by several veterans in sharing their first impressions of a defense geared toward creating mismatches by having players learn multiple roles. It's a distinct departure from the comparatively simple scheme they played last year under former coordinator Dave Wannstedt.

"Extremely different," defensive end Mario Williams said. "There's times, you know, I couldn't tell you what position I play exactly, because I really don't know."

Added veteran jack-of-all-trades linebacker Bryan Scott: "It's like I'm a rookie all over again. I had to go to Office Depot and get more flash cards."

Three weeks into spring minicamps, the questions become how quickly the Bills can adapt to yet another new system — their third in three years — and improve a unit that's been among the NFL's worst in yards and points allowed since 2010?

"It's all new, and I think they've done a good job of buying in," Pettine said. "We haven't given up a first down, a yard or a point. But I think we're off to a good start."

Entering his 12th NFL season, Pettine is part of the new staff assembled by rookie coach Doug Marrone, who was hired in January to replace Chan Gailey. Pettine came to Buffalo after holding the same job for the previous four seasons with the New York Jets.

In making the move upstate, Pettine gets an opportunity to come out of the shadow of longtime mentor, Jets coach Rex Ryan, who helped design the defense.

What's not changed is Pettine's attacking philosophy. He's brought to Buffalo a system featuring many of the same principles as the one that led to the Jets ranking in the NFL's top 10 in fewest yards allowed in each of the past four years.

Pettine's defense is not an easy one to label.

It's a hybrid, based upon a 3-4 (three-linemen, four-linebacker) philosophy, but can easily switch to a 4-3 or 5-2 look depending on the situation.

"I think the cornerstone of this system is flexibility," Pettine said. "A big part of the NFL is identifying pre-snap in a game. We want to limit the amount of pre-snap information we're putting out to an offense. And that's why we look for guys that have that type of versatility."

That objective is a reason why the Bills acquired linebacker Jerry Hughes in a trade three weeks ago that sent linebacker Kelvin Sheppard to Indianapolis. Hughes has experience playing several positions, while Sheppard was limited to playing the middle linebacker spot.

"Multiple guys doing multiple things," defensive end Mark Anderson said. "That's what's going to create that element of surprise. Offenses aren't going to know where the blitz is coming from. It's going to be just confusion out there."

Pettine is also counting on that confusion to help hide some of his unit's deficiencies.

The Bills are very young at linebacker, and preparing to give rookie second-round draft pick, Kiko Alonso, an opportunity to start. They also have questions in the defensive backfield, especially with star safety Jairus Byrd's status uncertain while he attempts to negotiate a new contract.

"We're going to be aggressive, relentless," Pettine said. "I think you can eliminate some of the youthful mistakes by putting pressure on people."

Center Eric Wood has faced enough of Jets' defenses over the past four seasons to know how disruptive they can be.

"It creates a ton of issues," Wood said.

He noted how Pettine's defense is already making it difficult on the offense to adapt to a new system of its own under Marrone and new coordinator Nathaniel Hackett.

"It's good that we're going through this now, because it'll make everything else seem a lot easier later," Wood said. "But in the immediate time, it's not always fun."

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NOTES: TE Scott Chandler is ahead of schedule recovering from surgery to repair a torn left knee ligament. Chandler has been running on his own for the past three weeks. After practice Thursday, he caught passes from rookie QB Jeff Tuel. ... NFL Players Association executive director DeMaurice Smith visited the Bills facility to watch practice and meet with players. ... The Bills are off until Tuesday, when they open a four-day voluntary minicamp.